Earth's formation is described as?

• A. Accumulation of dust and gas; collisions of smaller planetary bodies
• B. Quick cooling of a single large mass
• C. Gravitational collapse of a preexisting planet
• D. Fragmentation of a continental shield

Answer: (A)

Earth formed from the accretion of dust and gas in the early solar system, growing through collisions and sticking of smaller bodies in the protoplanetary disk. In the young Sun’s neighborhood, a rotating disk of material gradually clumped together as particles stuck together and later came under stronger gravity, pulling nearby material in and merging into larger bodies called planetesimals. These planetesimals collided and merged over millions of years, building up protoplanets and, eventually, the planets we know today. This gradual, collision-driven assembly explains why Earth is a product of dust and gas accumulation plus impacts, rather than a single quick cooling of a giant mass or the breakup of crustal blocks.

The other possibilities don’t fit Earth's formation history. A rapid cooling of a single large mass wouldn’t recreate Earth’s layered interior or long accretion process. Gravitational collapse of a preexisting planet would start with a planet already in place rather than forming one from the disk. Fragmentation of a continental shield describes later crustal tectonic processes, not the origin of Earth itself.